Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $244.60   7.384%   $262.6613   $262.66   $262.65   $262.70  
  Purchase #2 $60.65   13.493%   $68.8335   $68.83   $68.85   $68.80  
  Purchase #3 $24.74   5.399%   $26.0757   $26.08   $26.10   $26.10  
  Purchase #4 $104.77   12.775%   $118.1544   $118.15   $118.15   $118.20  
  Purchase #5 $76.78   8.552%   $83.3462   $83.35   $83.35   $83.30  
  Purchase #6 $52.50   5.799%   $55.5445   $55.54   $55.55   $55.50  
  Purchase #7 $154.93   7.728%   $166.903   $166.90   $166.90   $166.90  
  7 purchase totals = $718.97       $781.5186   $781.51   $781.55   $781.50